1. Field of the Invention
The present invention relates to a vehicle height adjust control apparatus and method that maintains the vehicle height at a target vehicle height.
2. Description of the Related Art
A conventional problem occurs when adjustment of a vehicle height to a target vehicle height is attempted while the vehicle is stopped with a brake pedal depressed. The vehicle height adjustment cannot be achieved because the wheels are prevented from rotating by arms between the vehicle body and the wheels that restrain the wheels and therefore prevent them from moving. However, pressure in the fluid pressure actuators for changing the vehicle height in normal conditions changes irrespective of a change in the vehicle height, so that when the brake pedal is released from the depression, the vehicle height is rapidly changed. To solve this problem, a vehicle height adjust control apparatus as described in, for example, Japanese Patent Application Laid-Open No. Hei 2-279410, suspends vehicle height adjust control under a condition as described above, or ceases the vehicle height adjust control if no substantial vehicle height change is achieved although the vehicle height adjust control is continued for a predetermined length of time. The aforementioned laid-open patent application also discloses a technology wherein while the wheels are restrained from rotating, the fluid pressure in the fluid pressure actuators is changed corresponding to the amount of shift of the actual vehicle height from the target vehicle height. This technology is intended to solve the problem that exists when the vehicle height adjustment is to be re-executed and the actual vehicle height is considerably deviated from the target vehicle height so that readjustment of the vehicle height needs to be performed and the convergence of the vehicle height to the target vehicle height is correspondingly delayed,
However, in real vehicles, it is possible, though it may be difficult, to change the vehicle height to some extent even while the vehicle is stopped with the brake pedal depressed, because the bushings and the like in the vehicular suspension devices can deform. In a case where the height of a vehicle is reduced due to an occupant or a luggage load added to the vehicle while the vehicle is stopped on a slope with the brake pedal operated, the re-starting of the vehicle without adjusting the vehicle height may result in a problem of the hitting of bound stoppers in the suspension devices or a problem of interference between a lower portion of the vehicle and bumps in a bad road. In such a situation, even though the vehicle is stopped with the brake pedal depressed, vehicle height adjustment is needed, and it is not preferable to entirely stop the vehicle height adjustment as in a conventional art.
Furthermore, in a conventional vehicle height adjust control apparatus wherein the control is ceased if no vehicle height change is achieved although vehicle height adjustment is continued for a set length of time as described above, the set length of time needs to be relatively long in order to set the vehicle height to a target vehicle height while the vehicle height is oscillating, for example, while the vehicle is running. However, if this set time is excessively long, the supply of fluid to fluid pressure actuators may continue for a long time while the vehicle height does not change. Conversely, if the set time is excessively short, the vehicle height may not be precisely or properly adjusted to a target vehicle height while the brake pedal is not operated, or almost no vehicle height change is caused while the brake pedal is depressed, so that the aforementioned problems of the hitting of bound stoppers and interference of a lower portion of the vehicle and a road surface may occur. Furthermore, in a conventional vehicle height adjust control apparatus wherein while the wheels are restrained from rotating, the fluid pressure in the fluid cylinders is changed corresponding to the amount of shift of the actual vehicle height from the target vehicle height as described above, it becomes necessary to use complicated component parts for regulating pressure, for example, pressure control valves and the like.